For the shortcomings and the insufficiencies in study of stride size of radially symmetrical hexapod robots, a workspace intersection method for parallel mechanism is proposed. In the method, the parallel mechanism composed of robot body, supporting legs and ground is divided into different branches, and according to the intersections of the workspaces of all the branches, and the stride size and stability margin of the robot can be deduced at any body height. By using this method, the maximum feasible stride size and stability margin can be obtained when the body height and the footholds are known. And its extreme stride size and the corresponding footholds at a certain body height can be solved. Meanwhile, the maximum stability margin and the corresponding suitable footholds can be determined while the stride size and body height are certain. This method provides a good reference for the radially symmetrical hexapod robot to choose suitable footholds, body height and stride size while walking in different gaits.